<!DOCTYPE html>
<html>
  <head>
    <title>盒子模型</title>
    <style>
      div{
        margin: auto;
      }
      .circle {
      width: 300px;
      height: 300px;
      background-color: white;
      border-radius: 50%;
      box-shadow: inset 50px 50px 100px rgb(56, 55, 55)   
    }
    </style>
  </head>
  <body>
    <br><br><br><br><br><br><br><br><br><br>
    <div class="circle"></div>
  </body>
</html>